Research Of Wheel Slip Ratio Control Based On Brake Actuator Characteristics

Vehicle chassis dynamics control has always been a hot research area in the automotive field in recent decades. Dynamic control systems such as anti-lock control, traction control and vehicle stability control have been widely used in real vehicles. We managed to implement these systems by means of controlling the tire force. There are some main factors influencing the tire force of vehicle, including the adhesion coefficient of road surface, wheel vertical load, wheel slip ratio, side-slip angle of the wheel, in which only the wheel slip ratio can be controlled. Therefore, slip ratio control is crucial for vehicle dynamics control. Vehicle dynamics control system can regulate tire force by controlling the slip ratio, whose adjustment rely on the control of wheel cylinder pressure. As a result we can manage wheel slip ratio around the target value by means of applying brake force to the controlled wheels in order to realize the adjustment of the tire force, and finally obtain the ideal vehicle dynamic performance. However, there are difficulties in the fine adjustment of wheel slip rate due to strong nonlinear characteristics of automobile brake actuator. Therefore, we can further improve the performance of chassis dynamics if integrated brake system features could be considered in the process of dynamic control and if cylinder pressure can be effectively estimated and finely adjusted.In this paper, the research work includes the following several parts:(1) This paper analyzed the structure and principles of the braking system, and established hydraulic brake system model which contains brake master cylinder, brake pipe, brake caliper, and wheel using the power bond graph theory, and thus the state equation which depicts the hydraulic brake system is deduced.(2) In this paper, we obtained experimental data of the braking system through hydraulic brake system test platform and finished parameters identification using the least square method and genetic algorithm.(3) Single wheel braking system model was built in AMESim. We compared the wheel cylinder pressure, electromagnetic valve flow curve obtained in the AMESim with that obtained in the bond graph model and thus verify the correctness of the bond graph model.(4) The wheel slip ratio controller based on the brake actuator characteristics was designed and off-line simulation verification was conducted through co-simulation platform of MATLAB and AMESim.